My guess is that either the upload failed (and now there are no files on the server), or you uploaded to the wrong folder. I just tried downloading the file in my browser and it returns a 404 as well. Make sure the file is on the actual server. Also, if you're using an IIS server you need to configure it to deliver .wys and .wyu files.
In other words, the error tells you exactly what's wrong -- the file was not found. Put the file on the server in the correct location and it will be found.